This invention relates to a process for the oligomerisation of at least one olefinic compound in the form of an olefin or a compound including an olefinic moiety by contacting the at least one olefinic compound with at least two different catalysts, namely a tetramerisation catalyst and a further oligomerisation catalyst. The tetramerisation catalyst comprises a combination of a source of a transition metal; and a ligating compound of the formula (R¹)_m X¹ (Y) X² (R²)_n. The invention also relates to an oligomerisation catalyst comprising the combination of (i) source of transition metal for both a tetramerisation catalyst and a trimerisation catalyst; (ii) a ligating compound for a tetramerisation catalyst; (iii) a differentligating compound for a trimerisation catalyst; and (iv) optionally an activator.